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<TITLE>Perfect Hash Function Generator - 2  Introduction</TITLE>
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<H1><A NAME="SEC3" HREF="gperf_toc.html#TOC3">2  Introduction</A></H1>

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<CODE>gperf</CODE> is a perfect hash function generator written in C++.  It
transforms an <VAR>n</VAR> element user-specified keyword set <VAR>W</VAR> into a
perfect hash function <VAR>F</VAR>.  <VAR>F</VAR> uniquely maps keywords in
<VAR>W</VAR> onto the range 0..<VAR>k</VAR>, where <VAR>k</VAR> &#62;= <VAR>n-1</VAR>.  If <VAR>k</VAR>
= <VAR>n-1</VAR> then <VAR>F</VAR> is a <EM>minimal</EM> perfect hash function.
<CODE>gperf</CODE> generates a 0..<VAR>k</VAR> element static lookup table and a
pair of C functions.  These functions determine whether a given
character string <VAR>s</VAR> occurs in <VAR>W</VAR>, using at most one probe into
the lookup table.

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<CODE>gperf</CODE> currently generates the reserved keyword recognizer for
lexical analyzers in several production and research compilers and
language processing tools, including GNU C, GNU C++, GNU Java, GNU Pascal,
GNU Modula 3, and GNU indent.  Complete C++ source code for <CODE>gperf</CODE> is
available from <CODE>http://ftp.gnu.org/pub/gnu/gperf/</CODE>.
A paper describing <CODE>gperf</CODE>'s design and implementation in greater
detail is available in the Second USENIX C++ Conference proceedings
or from <CODE>http://www.cs.wustl.edu/~schmidt/resume.html</CODE>.

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